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    <title>Document</title>
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<body>
    <script>
        let arr = [1,2,3,4,5,4,3,2,1]
        // 1.数组去重
        // let result = [...new Set(arr)]
        // console.log(result)

        // 2.交集
        let arr2 = [4,5,6,5,6]
        // let result = [...new Set(arr)].filter(item => {
        //     let s2 = new Set(arr2)
        //     if(s2.has(item)){
        //         return true
        //     }else {
        //         return false
        //     }
        // })
        // console.log(result)

        // 简化代码
        // let result = [...new Set(arr)].filter(item => new Set(arr2).has(item))
        // console.log(result)

        // 3.并集
        // let union = [...new Set([...arr,...arr2])]
        // console.log(union)

        // 4.差集
        let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)))
        console.log(diff)
    </script>
</body>
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